The problem exists that aquatic nuisance species (ANS) such as Zebra mussels are being transported between locations such as between ports of different countries in the ballast tanks of maritime vessels. Aquatic nuisance species may be defined as waterborne, non-native organisms that threaten the diversity or abundance of native species, the ecological stability of impacted waters or commercial, agricultural, aquacultural or recreational activities. A variety of measures for preventing invasion of an environment by ANS have been proposed, including purging of ballast tanks at sea before a vessel enters an area sensitive to ANS.
However, purging of a ballast tank requires emptying and refilling of the ballast tank. It will be understood that such a procedure can have an adverse effect on the stability of a vessel particularly in rough seas and is not appropriate in certain cases.